Mass analysis has been a basic technology to quantify molecular and atomic composition of various materials. Quantitative information obtained by mass analysis of molecules or atoms reveals chemical and physical characteristics of the materials. Today, three types of mass analyzers are commonly used in the field of mass analysis.
Magnetic sector analyzers disperse ions by mass utilizing magnetic force. The advantage of this type of analyzer is that each selected ion preserves its structure and feature as an ion beam. Magnetic sector analyzers work mainly in the range of mass under 10,000 Da, but should be bulky and heavy to analyze ions in the range over 10,000 Da.
A quadrupole mass analyzer comprises 4 rods on which DC (direct current) voltage and high frequency signals are applied. Only the ions of mass that match the electrical condition oscillate stably within the space surrounded by the 4 rods, pass through the space and arrive at the detector. Quadrupole mass analyzers work also in the range of mass under 10,000 Da. Although the resolution is not as high as magnetic sector analyzers, quadrupole mass analyzers are commonly used in research and industrial fields because they are compact and fairly easy to handle.
Time of flight (TOF) mass analyzers measure the transit time of ions utilizing the principle that the velocities of accelerated ions vary according to their mass. It goes without saying that TOF mass analyzers are noted for their wide mass range. As the upper limit of mass range depends on the length of the measurement time, it can be set long enough. On the other hand, this feature is the crucial point for this type of analyzers to raise their time efficiency, because the analyzers have to wait for the arrival of the heaviest pulsed ion at the detector for every measurement.
There are some other types of analyzers using rotating electric fields or time dependent electric fields for mass analysis, although they are not used as commonly as the three types of analyzers said above.
One attempt is found in U.S. Pat. No. 5,726,448, where ‘an ion beam is accelerated into the cell and the rotating electric field disperses the incident ion beam according to the mass to charge ratio and velocity distribution present in the ion beam’. A resolution is shown as ‘better than one part in 100 for a well defined beam’. Another ‘unique design’ is introduced in U.S. Pat. No. 6,794,647, where ‘a non-rotating, oscillating electric field that oscillates principally in a single coordinate plane’ select ions. Detailed description on mass resolution and mass range are not found, however. J. Kramer used ‘two identical deflectors’ and ‘one electrostatic lens’ located between the two deflectors to deflect ions. His instrument is described as ‘a time of flight mass spectrograph using a continuous ion beam’. J. H. Clemmons employed ‘a time-dependent electric field and a position-sensitive detector’. His instrument does not disperse ions, but determines the mass from detected particle position and detection time. K. Ohwaki's device ‘consists of two sets of electrodes that supply same sinusoidal electric field with same frequency but different phases and utilizes the difference of cluster velocity for selection’. As to mass resolution, however, it is estimated to be around 3 read from FIG. 4 in his paper.
During the past two decades, a great amount of new information and knowledge has been accumulated due to improved technologies of mass analysis, especially in the field of biochemistry and bio-medical research, and the tendency of using mass analysis of organic materials will grow enormously if an analyzer that fulfills all the functions and features of said analyzers is developed. The present invention is an improved versatile mass analyzer comprising two rotating electric fields and has features as follows:
1. An ability to analyze ion beams continuously as Magnetic sector mass analyzers do;
2. An ability to separate ions in the form of an ion beam as Magnetic sector mass analyzers do;
3. A compact and light weight body as Quadrupole mass analyzers have; and
4. An ability to analyze in the range of mass over 10,000 Da as TOF mass analyzers do.
More precise explanation will be made in the following Summary of Invention and Description of Embodiments.